The present invention relates to a simplified adaptive braking system that does not require wheel speed sensors.
Conventional antilock braking systems for road vehicles generally control braking action in response to a signal proportional to wheel speed. This signal is indicative of wheel slip, wheel acceleration and/or deceleration. Wheel speed is often generated by using wheel speed sensors and associated tone wheels for each controlled wheels or wheels of the vehicle. These wheel speed sensors are compared to control signals, the combination of which are utilized to sense wheel skid or impending skid and to appropriately control brake pressure so as to maintain the skidding wheel in a rotating condition. Ultimately one desires to control the skid and braking characteristic of each front and rear wheels of a vehicle such that each of the tires generate stopping forces which are as near the maximum attainable forces. These systems are characterized by the aforementioned wheel speed sensors and tone wheels, a plurality of isolation valves (in multi-channel systems), pressure decay valves and pressure release valves, which are each sequenced by a control unit. These all-wheel adaptive braking systems work adequately but present a relatively large cost to the vehicle owner.
Accordingly the invention comprises: A method and system for controlling the operation of vehicle brakes and associated wheels. The brake system includes a master cylinder controlled by the operator of the vehicle to vary applied brake pressure to various brake mechanisms during normal service brake operation and an antiskid brake subsystem, activated when one or more vehicle wheels are skidding, for controlling brake pressure in the various brake mechanisms to permit various wheels to operate in a nonskidding manner. The method comprises the steps of:
1.1) determining a control relationship k between vehicle deceleration and applied brake pressure, with none of the wheels of the vehicle skidding;
1.2) measuring at least two values (P.sub.1 P.sub.2) of applied brake pressure to determine a change in applied brake pressure .DELTA.P during a measurement interval;
1.3) calculating the change in control deceleration .DELTA.D.sub.ci corresponding to the change .DELTA.P in applied brake pressure utilizing the control relationship;
1.4) directly measuring actual vehicle deceleration D.sub.i ;
1.5) determining a change in actual vehicle deceleration .DELTA.D.sub.i corresponding to the change in applied brake pressure;
1.6) determining if the change in actual vehicle deceleration over the measurement interval is inconsistent with the change in control deceleration; and if such inconsistancy is determined:
1.7) reducing applied brake pressure to a determinable first level sufficient to cause actual vehicle deceleration to approach the control deceleration resulting from the reduced brake pressure.